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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Fencing affects movement patterns of two large carnivores in Southern Africa

The erection of peripheral fences around protected areas has been shown to adversely affect the movement behavior, genetic connectivity and long-term viability of animal populations. However, fencing is also used extensively to reduce human encroachment, limit poaching activities, and mitigate human–wildlife conflicts. Limited information on the movement behavior of carnivores is available along the periphery of protected areas, particularly in semi-arid environments. To quantify the potential effects of the 824 km perimeter fence surrounding the Etosha National Park (Etosha, Namibia) on the movement and space use of carnivores, we collected GPS movement data from 36 lions (Panthera leo) and seven spotted hyenas (Crocuta crocuta) over a 14-year period. For these two apex carnivores, we measured the impact of the Etosha fence on their movements (step lengths and path straightness), calculated the likelihood of fence crossings, and evaluated the spatial–temporal characteristics of these crossings. Our results indicated that lions and hyenas moved faster (longer step lengths) when closer to the fence. Lions showed no variation in path straightness with respect to the fence but hyenas had straighter movement paths when closer to the fence. When moving within the vicinity of the fence, lions had a 9% likelihood of crossing the fence, while hyenas were much more likely (18%) to do so, which suggests that the Etosha fence was more permeable for hyenas than for lions. Fence crossings predominantly occurred at night for both species. Lions were more likely to cross the fence during the cold dry season (May–August) whereas hyenas crossed more often during the warm wet season (December–April). Female and adult lions had a higher probability of crossing the fence than males and subadults. These findings could be useful in the development of appropriate strategies to mitigate human–carnivore conflicts and thus promote the conservation of carnivores in multiple-use areas along the periphery of the park. Further research is needed to better elucidate the impact of perimeter fences on a broader suite of carnivores and other large mammals, including species-specific variation in the response to fences, as well as the economic benefits of fencing provided to local communities.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2020

Phosphate tolerance of nitrogen-coordinated-iron-carbon (FeNC) catalysts for oxygen reduction reaction: A size-related hindrance effect

The greatest challenges facing the large – scale commercialization of the intermediate temperature phosphoric acid fuel cell (PAFC) technology are: (i) the high cost of Pt catalyst that is required to overcome the slow kinetics of oxygen reduction reaction (ORR) on the PAFC cathode, and (ii) deactivation of the Pt catalyst by exposure to the phosphoric acid electrolyte. Inexpensive carbon-based materials, particularly iron- spectroscopy is used to explore the phenomenon of phosphate poisoning nitrogen-coordinated carbon supported catalysts (FeNC), are promising cathodes for PAFCs. The higher ORR activation energy and phosphate poisoning resistance of FeNC present a clear advantage over the Pt-based commercial catalysts that are easily susceptible to deactivation after exposure to phosphate anions. While the immunity of FeNC catalysts to phosphate anion poisoning has been reported previously, this work explores the counter-intuitive and conditional nature of this poisoning resistance based on the properties of the carbon support used in the preparation of the FeNC catalyst. Additionally, a combination of electrochemical measurements with characterization experiments performed using X-ray photoelectron spectroscopy, infrared spectroscopy and in-situ X-ray absorption on FeNC catalysts synthesized from two different carbon supports. Results from these studies reveal a “size-related hindrance effect” wherein the ORR active Fe centers in FeNC remain inaccessible to larger anions such as phosphate when the Fe sites are present deeper inside the pores of a carbon support with high porosity. However, FeNC catalyst is poisoned by phosphate anions when synthesized using a carbon support with low porosity. This work helps gain insights into the nature of active sites in FeNC catalysts that will be useful in designing precious-metal free ORR catalysts for intermediate temperature fuel cell technologies.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1986

Basic studies on delta wing flow modifications by means of apex fences

The effectiveness of apex fences on a 60-deg delta wing at low speeds was experimentally investigated. Resembling highly swept spoilers in appearance, the fences are designed to fold out of the wing apex region upper surface near the leading edges, where they generate a powerful vortex pair. The intense suction of the fence vortices augments lift in the apex region, the resulting positive pitching moment being utilized to trim trailing edge flaps for lift augmentation during approach and landing at relatively low angles of attack. The fences reduce the apex lift at high angles of attack, leading to a desirable nose-down moment. The above projected functions of the apex fence device were validated and quantified through low speed tunnel tests, comprising upper surface pressure surveys on a semispan model and balance measurements on a geometrically similar fully span wing/body configuration. Fence parameters such as area, shape, hinge position and deflection angle were investigated. Typical results are presented indicating the apex fence potential in controlling the longitudinal characteristics of a tail-less delta.

Hoffler, K. D.↗
NASA NTRS1998

Tip Fence for Reduction of Lift-Generated Airframe Noise

The present invention is directed toward a unique lift-generated noise reduction apparatus. This apparatus includes a plurality of tip fences that are secured to the trailing and leading assemblies of the high-lift system, as close as possible to the discontinuities where the vortices are most likely to form. In one embodiment, these tip fences are secured to some or all of the outboard and inboard tips of the wing slats and flaps. The tip fence includes a generally flat, or an aerodynamically shaped plate or device that could be formed of almost any rigid material, such as metal, wood, plastic, fiber glass, aluminum, etc. In a preferred embodiment, the tip fences extend below and perpendicularly to flaps and the slats to which they are attached, such that these tip fences are aligned with the nominal free stream velocity of the aircraft. In addition to reducing airframe noise, the tip fence tends to decrease drag and to increase lift, thus improving the overall aerodynamic performance of the aircraft. Another advantage presented by the tip fence lies in the simplicity of its design, its elegance, and its ready ability to fit on the wing components, such as the flaps and the slats. Furthermore, it does not require non-standard materials or fabrication techniques, and it can be readily, easily and inexpensively retrofited on most of the existing aircraft, with minimal design changes.

Ross, James C.↗
NASA NTRS2016

Feasibility of Varying Geo-Fence Around an Unmanned Aircraft Operation Based on Vehicle Performance and Wind

Managing trajectory separation is critical to ensuring accessibility, efficiency, and safety in the unmanned airspace. The notion of geo-fences is an emerging concept, where distance buffers enclose individual trajectories and areas of operation in order to manage the airspace. Currently, the Air Traffic Management system for commercial travel defines static distance buffers around the aircraft; however, commercial UASs are envisioned to operate in significantly closer proximity to other UAS requiring a geo-fence for spacing operations. The geo-fence size can be determined based on vehicle performance characteristics, state of the airspace, weather, and other unforeseen events such as emergency or disaster response. Calculation of the geo-fence size could be determined as part of pre-flight planning and during real-time operations. A largely non-homogeneous fleet of UASs will be operating in low altitude and will likely be commercially developed. Due to intellectual property concerns, the operators may not provide detailed specifications of the control system to UTM. In addition, the huge variety of UAS makes modeling each control system prohibitive and flight data for these vehicles may not exist. Therefore, a generalized, simple geo-fence sizing algorithm must be developed such that it does not rely on detailed knowledge of the vehicle control system, accounts for the presence of urban winds, and is sufficiently accurate. In this work, two simple models are investigated to determine its feasibility as an adequate means for calculating the geo-fence size. The vehicle data used in this work are provided by UAS manufactures who have partnered with NASA's UTM project and some publicly available websites. The first model utilizes wind data processed from the NOAA HRRR (Hourly Rapid Refresh) product and Sonar Annemometer data provided by San Jose State. The second model utilizes OpenFOAM which is a CFD code used to generate a wind field for flow around a single building. The key vehicle performance parameters can include UAS response time to disturbances, command to actuation latency, control system rate limits, time to recovery to desired path, and aerodynamics. It was found that the first model provides an initial understanding of geo-fence sizing, but does not provide enough accuracy to provide UTM with an efficient means of scheduling vehicles. The results of the second model reveal that modeling UAS controls systems with a linearized plant and gain scheduled PID controller does not allow capture the UAS flight dynamics within a significant envelope of the wind disturbances.

uncertainty↗
NASA NTRS1985

An exploratory study of apex fence flaps on a 74 deg delta wing

An exploratory wind tunnel investigation was performed to observe the flow field effects produced by vertically deployed apex fences on a planar 74 degree delta wing. The delta shaped fences, each comprising approximately 3.375 percent of the wing area, were affixed along the first 25 percent of the wing leading edge in symmetric as well as asymmetric (i.e., fence on one side only) arrangements. The vortex flow field was visualized at angles of attack from 0 to 20 degrees using helium bubble and oil flow techniques; upper surface pressures were also measured along spanwise rows. The results were used to construct a preliminary description of the vortex patterns and induced pressures associated with vertical apex fence deployment. The objective was to obtain an initial evaluation of the potential of apex fences as vortex devices for subsonic lift modulation as well as lateral directional control of delta wing aircraft.

Wahls, R. A.↗
NASA NTRS1993

Reduction in size and unsteadiness of a VTOL ground vortex by ground fences

A ground vortex, produced when a jet impinges on the ground in the presence of cross flow, is encountered by V/STOL aircraft hovering near the ground and is known to be hazardous to the aircraft. The objective of this research was to identify a ground-based technique by which both the mean size and fluctuation in size of the ground vortex could be reduced. A simple passive method was identified and examined in the laboratory. Specifically, one or two fine wire mesh screens (ground fences) bent in a horseshoe shape and located on the ground in front of the jet impingement point proved to be very effective. The ground fences work by decreasing the momentum of the upstream-traveling wall jet, effectively causing a higher freestream-to-jet velocity ratio (V(sub infinity)/V(sub j)) and thus, a ground vortex smaller in size and unsteadiness. At(V(sub infinity)/V(sub j)) = 0.15, the addition of a single ground fence resulted in a 70 percent reduction in mean size of the ground vortex. With two ground fences, the mean size decreased by about 85 percent. Fluctuations in size decreased nearly in proportion to the mean size, for both the single and double fence configurations. These results were consistent over a wide range of jet Reynolds number (10(exp 4) less than Re(sub jet) less than 10(exp 5)); further development and full-scale Reynolds number testing are required, however, to determine if this technique can be made practical for the case of actual VTOL aircraft.

Cimbala, John M.↗
DOE OSTI2020

Mass production of high-performance single atomic FeNC electrocatalysts via sequenced ultrasonic atomization and pyrolysis process

Mass production of highly efficient, durable, and inexpensive single atomic catalysts is currently the major challenge associated with the oxygen reduction reaction (ORR) for fuel cells. In this study, we develop a general strategy that uses a simple ultrasonic atomization coupling with pyrolysis and calcination process to synthesize single atomic FeNC catalysts (FeNC SACs) at large scale. The microstructure characterizations confirm that the active centers root in the single atomic Fe sites chelating to the four-fold pyridinic N atoms. The identified specific Fe active sites with the variable valence states facilitate the transfer of electrons, endowing the FeNC SACs with excellent electrochemical ORR activity. The FeNC SACs were used as cathode catalysts in a homemade Zn-air battery, giving an open-circuit voltage (OCV) of 1.43 V, which is substantially higher than that of commercial Pt/C catalysts. This study provides a simple approach to the synthesis of single atomic catalysts at large scale.

36 MATERIALS SCIENCE↗
NASA NTRS1992

Lift augmentation on a delta wing via leading edge fences and the Gurney flap

Wind tunnel tests were conducted on two devices for the purpose of lift augmentation on a 60 deg delta wing at low speed. Lift, drag, pitching moment, and surface pressures were measured. Detailed flow visualization was also obtained. Both the leading edge fence and the Gurney flap are shown to increase lift. The fences and flap shift the lift curve as much as 5 deg and 10 deg, respectively. The fences aid in trapping vortices on the upper surface, thereby increasing suction. The Gurney flap improves circulation at the trailing edge. The individual influences of both devices are roughly additive, creating high lift gain. However, the lower lift to drag ratio and the precipitation of vortex burst caused by the fences, and the nose down pitching moment created by the flap are also significant factors.

Buchholz, Mark D.↗
NASA NTRS1993

Lift Augmentation on a Delta Wing via Leading Edge Fences and the Gurney Flap

Wind tunnel tests have been conducted on two devices for the purpose of lift augmentation on a 60 deg delta wing at low speed. Lift, drag, pitching moment, and surface pressures were measured. Detailed flow visualization was also obtained. Both the leading edge fence and the Gurney flap are shown to increase lift. The fences and flap shift the lift curve by as much as 5 deg and 10 deg, respectively. The fences aid in trapping vortices on the upper surface, thereby increasing suction. The Gurney flap improves circulation at the trailing edge. The individual influences of both devices are roughly additive, creating high lift gain. However, the lower lift to drag ratio and the precipitation of vortex burst caused by the fences, and the nose down pitching moment created by the flap are also significant factors.

Buchholz, Mark D.↗
NASA NTRS1959

A Buffet Investigation at High Subsonic Speeds of Wing-Fuselage-Tail Combinations having Sweptback Wings with NACA Four-Digit Thickness Distributions, Fences, and Body Contouring

An investigation has been made to determine the effect of wing fences, fuselage contouring, varying wing sweepback angle from 40 deg. to 45 deg., mounting the horizontal tail on an outboard boom) and wing thickness distribution upon the buffeting response of typical airplane configurations employing sweptback wings of high aspect ratio. The tests were conducted through an angle-of-attack range at Mach numbers varying from 0.60 to 0.92 at a Reynolds number of 2 million. For the combinations with 40 deg. of sweepback, the addition of multiple wing fences usually decreased the buffeting at moderate and high lift coefficients and reduced the erratic variation of buffet intensities with increasing lift coefficient and Mach number. Fuselage contouring also reduced buffeting but was not as effective as the wing fences. At most Mach numbers, buffeting occurred at higher lift coefficients for the combination with the NACA 64A thickness distributions than for the combination with the NACA four-digit thickness distributions. At high subsonic speeds, heavy buffeting was usually indicated at lift coefficients which were lower than the lift coefficients for static-longitudinal instability. The addition of wing fences improved the pitching-moment characteristics but had little effect on the onset of buffeting. For most test conditions and model configurations, the root-mean- square and the maximum values measured for relative buffeting indicated similar effects and trends; however, the maximum buffeting loads were usually two to three times the root-mean-square intensities.

Sutton, Fred B.↗
NASA NTRS1975

Plasma confinement by a picket-fence

It is shown that a current-produced line cusp field in a 'picket fence' configuration will confine both primary ionizing electrons and plasma. The 'picket fence' consists of a planar array of equally spaced water-cooled copper tubing with the current alternating in direction. The loss rates of both plasma and primary electrons are shown to be inversely proportional to the fence current. Plasma confinement is found to be much weaker than electron confinement.

Leung, K. N.↗
NASA NTRS1985

An experimental investigation of apex fence flaps on delta wings

The effects on leading edge vortex formation produced by apex fences mounted on two delta wings were examined in a subsonic wind tunnel. Pressure data were collected on the upper surface of the test wings and oil flow and bubble flow visualizations were performed. The deflections studied were 74, 90 and 65 deg in one-sided and two-sided configurations. Full span and semi-span delta wing planforms were used. Relatively small, symmetrically deployed apex fences provided enhanced upper surface suction which, in some angle-of-attack situations, could lead to a pitch-up force. Asymmetrically-deployed fences showed promise for yaw control at high angles of attack, althouh the force effectiveness has yet to be quantified.

Vess, R. J.↗
NASA NTRS1992

CFD analysis on control of secondary losses in STME LOX turbines with endwall fences

The rotor blade in the newly designed LOX turbine for the future Space Transportation Main Engine (STME) has a severe flow turning angle, nearly 160 degrees. The estimated secondary loss in the rotor alone accounts for nearly 50 percent of the total loss over the entire stage. To reduce such a loss, one of the potential methods is to use fences attached on the turbine endwall (hub). As a prelude to examining the effects of endwall fence with actual STME turbine configuration, the present study focuses on similar issues with a different, but more generic, geometry - a rectangular duct with a 160-degree bend. The duct cross-section has a 2-to-1 aspect ratio and the radii of curvature for the inner and outer wall are 0.25 and 1.25 times the duct width, respectively. The present emphasis lies in examining the effects of various fence-length extending along the streamwise direction. The flowfield is numerically simulated using the FDNS code developed earlier by Wang and Chen. The FDNS code is a pressure based, finite-difference, Navier-Stokes equations solver.

Chyu, Mingking K.↗
NASA NTRS1991

Swept wing attachment line contamination fence

A device for controlling attachment line contamination on an airfoil is presented. A fence is installed on the leading edge of the airfoil in the freestream direction perpendicular to the airfoil, outboard of the fuselage boundary layer. The inboard side of the fence arrests the spanwise movement of the turbulent boundary layer while the laminar boundary layer on the outboard side of the fence eliminates any further turbulent contamination of the attachment line.

Holmes, Bruce J.↗
NASA NTRS1954

Wind-Tunnel Investigation at Low Speed of the Effects of Chordwise Wing Fences and Horizontal-Tail Position on the Static Longitudinal Stability Characteristics of an Airplane Model with a 35 Degree Sweptback Wing

Low-speed tests of a model with a wing swept back 35 degrees at the 0.33-chord line and a horizontal tail located well above the extended wing-chord plane indicated static longitudinal instability at moderate angles of attack for all configurations tested. An investigation therefore was made to determine whether the longitudinal stability could be improved by the use of chordwise wing fences, by lowering the horizontal tail, or by a combination of both. The results of the investigation showed that the longitudinal stability characteristics of the model with slats retracted could be improved at moderate angles of attack by placing chordwise wing fences at a spanwise station of about 73 percent of the wing semispan from the plane of symmetry provided the nose of the fence extended slightly beyond or around the wing leading edge.

Queijo, M J↗
NASA NTRS2016

Assessment of Fencing on the Orion Heatshield

This paper presents recent experimental results from arc-jet tests of the Orion heatshield that were conducted at NASA Ames Research Center. Test conditions that simulated a set of heating profiles in time representative of the Orion flight environments were used to observe their effect on Orion's block architecture in terms of differential recession or fencing. Surface recession of arc-jet models was characterized during and after testing to derive fencing profiles used for the baseline sizing of the heatshield. Arc-jet test data show that the block architecture produces varying degrees of fencing.

Ground tests↗
DOE OSTI2021

Improved Bounds for Burning Fence Graphs

Graph burning studies how fast a contagion, modeled as a set of fires, spreads in a graph. The burning process takes place in synchronous, discrete rounds. In each round, a fire breaks out at a vertex, and the fire spreads to all vertices that are adjacent to a burning vertex. Additionally, the burning number of a graph G is the minimum number of rounds necessary for each vertex of G to burn. We consider the burning number of the \(m \times n\) Cartesian grid graphs, written \(G_{m,n}\) . For \(m = \omega (\sqrt{n})\) , the asymptotic value of the burning number of \(G_{m,n}\) was determined, but only the growth rate of the burning number was investigated in the case \(m = O(\sqrt{n})\) , which we refer to as fence graphs. We provide new explicit bounds on the burning number of fence graphs \(G_{c\sqrt{n},n}\) , where \(c > 0\) .

79 ASTRONOMY AND ASTROPHYSICS↗